Incorporation of silica into a rubber composition that constitutes a tread portion has heretofore been performed as a method for maintaining wet grip performance and at the same time reducing rolling resistance. Moreover, in order to further reduce the rolling resistance, a tire in which silica has been incorporated into the rubber composition constituting its sidewall portion has, for example, been researched (Japanese Patent Laying-Open No. 10-036559 (Patent document 1)).
However, in the case when a large amount of silica is contained, the electric resistance of the tire is increased and, therefore, there is a possibility that a spark might be generated due to static electricity to cause the fuel to catch fire, for example, during refueling for a vehicle, resulting in a safety hazard in use; therefore, there have been strong demands for provision of tires with which the reduction in the rolling resistance and the maintenance of the wet grip performance are realized and generation of static electricity is sufficiently prevented.
For example, Japanese Patent Laying-Open No. 8-034204 (Patent document 2) discloses a method in which a rubber with a low electric resistance is buried in a tread portion as a method for reducing the static electricity. This, however, has resulted from the study of the electric resistance problem in a tread, and is not capable of imparting an excellent rolling resistance and a sufficiently reduced electric resistance to a tire in which silica is blended also to the sidewall portion and the breaker portion as described above.
Patent document 1: Japanese Patent Laying-Open No. 10-036559
Patent document 2: Japanese Patent Laying-Open No. 8-034204